The present invention concerns a polarization separator for separation/combination of orthogonally polarized high-frequency waves, guided in a waveguide, which is usable for extremely large bandwidth.
Different variants are known for combination and separation of orthogonally polarized signals. A review of designs of such polarization separators or combiners is offered in xe2x80x9cWaveguide Components for Antenna Feed Systems: Theory and CADxe2x80x9d, Artech House, 1993, pages 377 ff.
Since polarization separators and combiners do not differ in design, but only in the direction in which they are traversed by the electromagnetic wave, the term xe2x80x9cpolarization separatorxe2x80x9d is used below for both.
Simple designs are obtained, if only the fundamental wave types H10and H01 are capable of propagation in the common connection waveguide, on which the polarization separator is mounted. This constraint limits the useful frequency band of such variants to about 25%.
Polarization separators with a bandwidth of more than 30% require more demanding designs, in which coupling of higher wave types, capable of propagation in the connection wave guide, is suppressed, because of the symmetry in the branching region of the separator. On page 397 of the aforementioned literature source, a polarization separator with such a symmetric layout is depicted, which has an input section, in which orthogonally polarized wave types are capable of propagating, two first output sections separated by a septum and extending in an extension of the input section for a first of the wave types, and two second output sections extending sideward in the plane of the septum for the second wave type. This design corresponds to a five-gate waveguide branch with two symmetric waveguide pairs that correspond to the first and second output sections, in which the fundamental wave type of each of these output sections couples half of the signal energy of the corresponding polarization of the input section. The first and second output sections are decoupled from each other. The first and second output sections can be combined by appropriate means, like branches, a magic T, etc., so that the two orthogonal polarizations can each be tapped at a terminal or fed into a connection wave guide, when the polarization separator is used to combine two orthogonal polarizations.
The maximum attainable useful bandwidth in this known polarization separator is limited to about 50%. The reason for this is that the wave types within the paired symmetric connection section, whose electromagnetic fields are oriented orthogonal to the corresponding fundamental wave type, are capable of propagation when the frequency of the wave exceeds twice the limiting frequency of the corresponding connection section. If, however, the connection waveguide is capable of transmitting the orthogonal polarization, this principle is no longer applicable, since the short circuit planes required for the wave types are no longer present in the branching zone.
A polarization separator that has ridges on the inside surface of its input section and on four connection sections extending in an extension of the inside wall is known from GB 2 175 145.
The design of this polarization separator is demanding and the fact that all four output sections have the same orientation parallel to the axis of the input section makes the use of complicated connection conductors, oscillated in several planes, essential, in order to combine the orthogonal polarization component occurring at the two output sections.
With the present invention a polarization separator is devised, with which the orthogonal wave types of a common waveguide connected to an input section of the polarization separator can be coupled independently in a very broad frequency band. The width of the frequency band can be 56% and more.
This advantage is achieved in a polarization separator with an input section in which orthogonally polarized wave types are capable of propagating, and two first output sections separated by a septum and extending in an extension of the input section for a first wave type, and two second output sections extending sideward in a plane of the septum for the second wave type, by the fact that the second output sections are designed as coaxial conductors. The septum means that, of the two orthogonally polarized wave types H10, H01 that are capable of propagation in the input section, the one with an E field parallel to the orientation of the septum is reflected. A short circuit plane is therefore formed for this wave type, so that coaxial conductor coupling is carried out at the corresponding field strength maximum in front of the septum. In order to achieve coupling of the wave types with an E field perpendicular to the septum to the first output sections with the lowest possible reflection, it is expedient for the septum to have a front section that tapers into the input section. The second output sections then lead into the input section appropriately between the tip and base of the front section.
In order to increase the uniqueness range of the polarization separator, it is expedient to provide its input section on its walls with inward protruding ridges oriented in the longitudinal direction.
These ridges are expediently lengthened into the first output section on those walls of the input section to which the second output section does not lead, in order to also increase its uniqueness range.
A waveguide provided with such ridges has a lower limiting frequency than a waveguide without the ridges with the corresponding dimensions. The uniqueness range of the waveguide with ridges is therefore greater.
If the input section has no ridges, but the first output sections are designed with ridges because of the large bandwidth, it is expedient to provide a step at the transition between the input section and the first output sections, in which the ridges extend from the step only over part of the length of the input section. The cross section can then be expediently dimensioned, so that the limiting frequencies of the ridgeless part of the input section and the first output sections are the same.
Additional features and advantages of the invention are apparent from the following description of practical examples with reference to the figures.